Immobilizers are devices on motor vehicles that are intended to prevent their unauthorized use. One generally distinguishes between electronic and mechanical immobilizers.
Electronic immobilizers are required by law in many countries. These electronic immobilizers include, among other things, so-called three-circuit interceptors that short-circuit the ignition, the fuel supply and the starter with the aid of a relay. Other known electronic immobilizers access the engine control unit and issue a clearance, without which the engine will not start. The communication of corresponding clearances usually takes place via a bus system of the motor vehicle and is encrypted. Immobilizers are frequently unlocked by radio transmitters that are typically integrated into keys—in the colloquial sense—of the motor vehicle and act as transponders. The communication may take place in encrypted or unencrypted form.
Mechanical immobilizers may consist, for example, of steering wheel clamps, steering wheel locks, wheel boots or the like. In addition, immobilizers may also feature a mechanical component such as, for example, a steering wheel locking system that is controlled by the immobilizer control and blocks the further use of a motor vehicle steering system. The incorporation of a mechanical immobilizer requires a certain vehicle complexity that increases the development effort, as well as the costs of the motor vehicle.